This invention relates to the filed of electrocardiography and more specifically to a method and apparatus for analyzing electrocardiogram and its serial changes, including small changes that cannot be exposed by conventional analysis, structuring and representing the results in the form understandable both to lay public and medical professionals.
Electrocardiogram is one of the most common medical examinations of cardiac electrical activity, which is performed by a medical professional or paramedics. Registration of ECG is relatively simple, however, its analysis requires a highly qualified physician with substantial experience in electrocardiography.
In general, there are two types of ECG tests, a one-time recording during a few seconds and a long-term monitoring which can be performed during various physiological tests, regular daily activities or as a round-the-clock monitoring in patients with serious medical disturbances. Each test requires a specialized protocol for registering and analyzing ECG signals.
One-time ECG recording is usually performed by ECG technicians or paramedics. The recording then is transferred to a physician for analysis, which includes a number of procedures. First, the cardiac complexes are visually identified by their characteristic shape consisting of a sequence of the following waves: P-, Q-, R-, S-, T- and sometimes U-wave. Next, these complexes are classified according to their origin as normal or sinus, supraventricular, ventricular complexes and their subtypes. The distance between two consecutive complexes is measured to determine the heart rate. Next, a number of the most important parameters including the amplitudes of each wave, the duration of PQ, QRS, and QT-intervals, and the amplitude of ST-segment are measured. Finally, the signals are compared with the recordings that were previously obtained from the same patients to determine serial changes in cardiac electrical activity.
Comparison of serial recordings is an important part of standard ECG examination that allows detection of changes and determining their time course. The comparison is performed visually by an experienced medical professional. The accuracy of this subjective comparison is not high and varies among physicians. The accuracy is not stable even in the same physician when the same measurements are repeated several times.
There are a number of prior art computerized systems that follow these basic steps of analysis and measure characteristic waves of ECG and prepare preliminary report for physicians. Since the number of analyzed variables and their combinations is large, these systems use sophisticated processing algorithms that require fast and powerful microprocessors or computers with a large memory available for processing.
Systems for long-term monitoring consist of two types, recording and real-time systems. Recording systems include 24-hour Holter monitors and event monitors, which record the data after a manual signal (event). Processing of these recordings, which include a large amount of data, consists of computer-assisted scanning with subsequent manual verification by an experienced medical professional. The results of analysis which include average heart rates, number of normal and types of abnormal beats during different periods of time, are submitted to a physician for final verification and conclusion.
Real-time systems include event-monitors, bedside monitors, stress-test systems and other devices for monitoring 1-2 critically important parameters and generating alarm or presenting the output information on a monitor. These systems perform an incomplete examination tracking the changes in heart rate and sometimes changes in the ST-segment. While this information is important for real-time control of a test or treatment, a number of important ECG changes, including changes in Q-, T-, or P-wave amplitude, QT-duration, are not exposed by this analysis.
It is known to provide portable ECG monitors that will sound an alarm or other signal to alert the user or an attendant of abnormal or unusual changes in the waveforms of the ECG signal. Such devices are, for example, disclosed in U.S. Pat. Nos. 4,193,393; 4,679,144; 5,033,475; 5,501,229 and 5,724,983. A system is also known, from U.S. Pat. No. 6,038,469, that includes at least one monitoring module for receiving ECG signals, a circuit for analyzing the signal, a plurality of parameters related to a patient""s ischemic condition, and a network for exchanging data with a central unit, either by hard wire or telemetry. The monitor can be used in an ambulatory application in which the ECG signals are recorded and later sent to a central processing unit or units, which may be capable of sending information and data to the portable unit(s).
Shusterman et al. U.S. Pat. No. 5,967,995 has identified small cumulative changes in the series of cardiac inter-beat intervals using the Principal Component Analysis (PCA). This method accurately identified unstable dynamics of cardiac rhythm and predicted cardiac arrhythmias as early as several hours before the processing event when all known physiological indicators remained normal. The Shusterman et al. invention further extends the applications of PCA to the ECG signal.
This invention provides a portable and easy-to-use system for structured and complete analysis and representation of electrocardiogram and its serial changes quantitatively for medical professionals and qualitatively for a lay patient who does not have any medical background. Structuring of the analysis is achieved by constructing the at least two, and preferably three, information scales that represent the most significant parameters at different level of detail.
Low, intermediate and high-resolution scales are defined according to the corresponding software and hardware resources. A low-resolution (Scale I) represents a small number of the most important primary elements such as intervals between the heart beats, duration of PQ, QRS, and QT-intervals, amplitudes of P-, Q-, R-, S-, and T-waves. This real-time analysis is implemented in a portable device that requires minimum computational resources. The set of primary elements and their search criteria are adjusted for each ECG utilizing computational resources of intermediate or high-resolution levels. At the intermediate-resolution (Scale II), serial changes in each of the said elements are determined using a mathematical decomposition into series of orthogonal basis functions and their coefficients. This scale is implemented using a specialized processor or a computer organizer. At the high-resolution (Scale III), serial changes in all elements of the ECG and their combinations are extracted using orthogonal mathematical decomposition to provide complete information about the dynamics of the signal. This scale is implemented using a powerful processor, a network of computers or the Internet.
Scale I may be implemented in a portable, pocket-size device, in which the signal is decomposed into a plurality of primary elements and parameters such as intervals between the heart beats, type of a cardiac complex, amplitudes and duration of P-, QRS, T-, and U-wave, QT-interval, amplitude of ST-segment. Scale I of the system provides the means for real-time electrocardiographic analysis by comparing the primary elements of ECG with reference values (individual thresholds) using the minimum computational resources. The reference values are programmed into the device based on normal values for the primary elements for the patient. Scale I includes means for adjustment of individual thresholds and criteria for rejection of noisy data. A detector of noise and error rejects the noisy data if the primary elements exceed physiologic range. Alternatively, modification of the primary elements and adjustment of their search criteria can be performed automatically at the higher-resolution Scale II or Scale III. In this case, the Scale I analysis is implemented using a programmable microprocessor that can be reprogrammed at the higher-resolution scales to account for the individual characteristics of the ECG pattern and monitoring goals. Specific sets of primary elements can be used for patients with different cardiovascular abnormalities.
Scale I can be used in two modes: static mode and dynamic mode. The static mode is used for one-time ECG examination in which the newly acquired primary elements are compared with the default reference values. The dynamic mode is used for comparison of the newly acquired primary elements and waveforms with the primary elements and waveforms that were previously acquired from the same person. The shapes of QRS, T, and P-waves are compared using cross-correlation function. A small magnitude of the difference between the two measurements permits classifying them as substantially similar and keeping only one measurement in the memory.
Scale I provides sufficient information for standard, one-time, clinical ECG examination. The most significant primary elements may be represented as a color, symbol, or other easy-to-read encoding of indicators that make the results useful and understandable for a lay person and a medical professional. Each signal-indicator corresponds to a single primary element. In the static mode, the values of the indicators are preferably color-coded for a lay person into normal, moderately or severely abnormal. This representation constitutes a static screen. Alternatively, the indicators may be symbol-coded, N for normal and A for abnormal reading; they may vibrate or produce a sound output for people with vision or hearing impairments. For a medical professional, the indicators provide exact, quantitative values of the primary elements. In the dynamic mode, the indicators are preferably symbol (or color)-coded into C for changed or U for unchanged. This representation constitutes a dynamic screen.
Intermediate-resolution Scale II allows viewing the ECG with automatically determined primary elements on a display and interactive editing of the set of primary elements and their search criteria. The editing can be performed by a user or a medical professional to modify the set of characteristic points or to adjust their search criteria, and can be performed either manually or automatically by the software. The individually adjusted search criteria can then be used to re-program the Scale I analysis as described earlier.
Scale II allows accurate comparison of serial ECGs and detection of small serial changes that may be unexposed by visual inspection of the signals. This scale requires higher computational resources than Scale I and can be implemented in a specialized processor, computer organizer or a personal computer. These computational resources also allow manual entering text information about the patient into the database and specific instructions regarding adjustment of time windows, threshold values, and other variables. To perform the Scale II analysis, the primary elements from serial ECGs are stored into a database to construct the time series for each primary element. The series is decomposed into a few most significant basis functions and coefficients using Principal Component Analysis (PCA) or any other orthogonal set of basis functions. The newly acquired values of the primary elements are compared with the series of the previously obtained values. Furthermore, the changes in the series of PCA coefficients are analyzed to detect small cumulative changes in the dynamics of the series that indicate instability in the cardiac electrical activity.
High-resolution Scale III is used to analyze individual and combined changes in the primary elements; at this scale, the number of the primary variables is increased to include the entire waveform of the cardiac complexes. This allows the most sensitive and accurate detection of the small changes in the individual electrocardiographic pattern. The same PCA approach is used at this scale to expose small serial changes in the ECG recordings. Scale III requires higher computational resources compared to Scale I and Scale II; it may be implemented in a powerful processing unit such as a personal or specialized computer or a distributed network of computers or the Internet.
This invention can be used for one-time examinations by patients, medical professionals, paramedics and lay public, and for dynamic assessment of changes in cardiac electrical activity. The information can be transmitted to an external computer system or a network of computers. For a lay person, the system may also include a database explaining significance of the changes in each primary element and providing simple recommendations about the measures that has to be taken if the readings of the indicators become abnormal. These may include complete cessation of physical activity, contacting a medical professional, taking a medication, etc. More detailed recommendations might be provided for patients who have specific abnormalities or medications. These patients might require special monitoring or individual adjustment of their primary elements. For example, specific monitoring the duration of QT-interval is important in patients taking antiarrhythmic drugs that prolong QT-interval.
The system can be used as
first-aid ECG analyzer for emergency units, paramedics, and medical personnel;
ECG analyzer for a routine medical examination;
a personal one-time or serial ECG analyzer with storage of individual electrocardiographic historic data, adaptive adjustment of individual thresholds and assessment of changes in individual ECG pattern;
a one-time or serial ECG analyzer for a group of people, a family or a patient group, with storage of individual electrocardiographic historic data for each person, adjustment of individual thresholds and assessment of changes in individual ECG patterns;
event-monitoring device including patient-detected events, changes in heart rate or ST-segment;
arrhythmia, bed-side, stress-test monitoring;
pacemaker and other implantable device checking;
evaluation of the treatment efficacy, side effects and progression of the disease.
Accordingly, an object of this invention is to provide a system for analyzing ECG signals at least at two levels of detail or resolution. Both levels of resolution are presented in simple representation that can be understood by lay persons, as well as medical professionals.
A further object of this invention is to provide an ECG analyzing system that includes a monitoring device for receiving and analyzing ECG signals and which includes means for communicating with an external computer to which the ECG signals can be forwarded for more complex analysis. The monitoring device can be reprogrammed by the external computer to select the primary elements of the ECG signals that are unstable or abnormal. The low level analysis performed by the monitoring device is thus focused on the critical primary elements for that patient.
The above and other objects and advantages of this invention will be more fully understood and appreciated by reference to the following description and the drawings.